1. Field of the Invention
The present invention relates to a surface-discharge type AC plasma display panel (hereinafter, referred to as xe2x80x9cAC-PDPxe2x80x9d), and more particularly to a method of driving the AC-PDP and a driving circuit therefor.
2. Description of the Background Art
A variety of studies has been made in a field of PDP (Plasma Display Panel) used as a slim television or display monitor. One of AC-PDPs having a memory function is a surface-discharge type AC-PDP, and structure and driving method of the PDP will be discussed below with reference to FIGS. 32 and 33A to 33E.
FIG. 32 is a perspective view showing a structure of a surface-discharge type AC-PDP in the prior art, and the surface-discharge type AC-PDP having this structure is disclosed in Japanese Patent Application Laid Open Gazettes 7-140922 and 7-287548. In FIG. 32, a surface-discharge type AC-PDP 101C comprises a front glass substrate 102C serving as a display surface and a rear glass substrate 103C opposed to the front glass substrate 102C with a discharge space therebetween. On a surface of the front glass substrate 102C on the side of the discharge space, n first electrodes 104C and n second electrodes 105C are extendedly provided in pairs. As shown in FIG. 32, when the first and second electrodes 104C and 105C have metal assistant electrodes (bus electrodes) on part of their surfaces, respective electrodes including the metal assistant electrodes may be termed xe2x80x9ca first electrode 104Cxe2x80x9d and xe2x80x9ca second electrode 105Cxe2x80x9d. Further, the first and second electrodes 104C and 105C are also termed row electrodes 104C and 105C, respectively. In the AC-PDP 101C, a dielectric layer 106C is so provided as to cover the row electrodes 104C and 105C. In some cases, as shown in FIG. 32, an MgO film 107C made of MgO (magnesium oxide) which is a dielectric is formed by evaporation on a surface of the dielectric layer 106C. In this case, the dielectric layer 106C and the MgO film 107C are termed xe2x80x9cdielectric layer 106ACxe2x80x9d as a unit.
On a surface of the rear glass substrate 103C on the side of the discharge space, m third electrodes 108C (hereinafter, referred to as xe2x80x9ccolumn electrode 108Cxe2x80x9d) are so provided extendedly as to cross the row electrodes 104C and 105C. Between adjacent column electrodes 108C, a barrier 110C is extendedly provided in parallel to the column electrodes 108C. The barrier 110C separates discharge cells and works as a pole for supporting the PDP lest the PDP should be broken by atmospheric pressure. On a surface of the column electrode 108C and a side-wall surface of the barrier 110C, phosphor layers 109C for emitting red, green and blue lights are provided orderly in stripes.
The front glass substrate 102C and the rear glass substrate 103C having the above structure are sealed to each other, and in a space between these glass substrates 102C and 103C, a discharge gas such as an Nexe2x80x94Xe mixed gas and Hexe2x80x94Xe mixed gas is enclosed by a pressure not more than atmospheric pressure. In the surface-discharge type AC-PDP 101C having this structure, the discharge space comparted by the row electrodes 104C and 105C in a pair and the column electrodes 108C is a discharge cell for the PDP 101C, i.e., a pixel.
Next, a principle of a display operation of the above prior-art PDP will be discussed.
First, a voltage pulse is applied to the row electrodes 104C and 105C to cause a discharge. An ultraviolet ray generated by this discharge excites the phosphor layer 109C, to cause the discharge cell to emit. In this discharge, electrons and ions generated in the discharge space move to the row electrodes 104C and 105C of reverse polarity and are stacked on a surface of the dielectric layer 106AC on the row electrodes 104C and 105C. The electrons and ions stacked on the surface of the dielectric layer 106AC are termed xe2x80x9cwall chargesxe2x80x9d. The amount of wall charges depend on an externally-applied voltage value and therefore a potential of the wall charges can not exceed the externally-applied voltage value.
An electric field induced by the wall charges works to weaken an applied electric field and therefore the discharge rapidly disappears as the wall charges are generated. After the discharge disappears, when a voltage pulse of reverse polarity is applied between the row electrodes 104C and 105C, a discharge occurs again since an electric field in which the applied electric field and the electric field induced by the wall charges are superposed is substantially applied in the discharge space. Thus, once a discharge occurs, successive discharge can be caused by applying an applied voltage (hereinafter, referred to as xe2x80x9csustain voltagexe2x80x9d) lower than the voltage at the time when the discharge starts. Therefore, applying the sustain voltage (hereinafter, referred to also as xe2x80x9csustain pulsexe2x80x9d) between the row electrodes 104C and 105C with its polarity reversed alternately makes it possible to stationarily sustain the discharge. Hereinafter, the discharge is referred to as xe2x80x9csustain dischargexe2x80x9d.
The sustain discharge can be kept as far as the sustain pulse is applied until the wall charges disappear. Extinguishing the wall charges is referred to as xe2x80x9cerasexe2x80x9d and generating the wall charges on the dielectric layers 106AC (MgO film 107C) in the initial stage of the discharge is referred to as xe2x80x9cwritexe2x80x9d. With respect to any cell in a screen of the AC-PDP, write is first performed, and thereafter the sustain discharge is performed, to display characters, figures and images. Performing quick operation of the write, sustain discharge and erase allows display of motion pictures.
According to the above principle of operation, in the discharge on the rise of the applied pulse, the effective voltage consists mainly of the externally-applied voltage and supplementally of the wall charges. Therefore, this discharge is termed xe2x80x9cdischarge mainly induced by externally-applied voltagexe2x80x9d.
On the other hand, if the externally-applied voltage is very high, in some times, the wall charges produce a potential not less than the firing voltage. In this case, on the fall of the applied pulse, the discharge can occur only by the wall charges. The discharge with no voltage externally applied is referred to as xe2x80x9cself-erase dischargexe2x80x9d. Since the effective voltage of the discharge is given mainly by the wall charges, the discharge is referred to as xe2x80x9cdischarge mainly induced by wall chargesxe2x80x9d. Since the externally-applied voltage may be supplementally applied in a direction to increase the discharge in the discharge mainly induced by wall charges, the definition of xe2x80x9cdischarge mainly induced by wall chargesxe2x80x9d herein includes the discharge with the supply of the external voltage.
When the AC-PDP is driven by using both the xe2x80x9cdischarge mainly induced by externally-applied voltagexe2x80x9d and the xe2x80x9cdischarge mainly induced by wall chargesxe2x80x9d, since the wall charges are reduced after termination of the discharge mainly induced by wall charges, in order to subsequently cause the discharge main induced by externally-applied voltage, it is necessary to (i) apply higher externally-applied voltage or (ii) apply the externally-applied voltage in a state where the firing voltage is lowered by the space charges generated in the discharge mainly induced by wall charges. Especially, the case (ii), i.e., the driving method using the pulse memory effect can lower a current density per one discharge, and can thereby improve a discharge efficiency and reduce a peak current value. Further, the discharge mainly induced by wall charges ends with a certain amount of wall charges according to the discharge characteristics of the cell even if a voltage variation exists in the panel. Hence, when the discharge mainly induced by externally-applied voltage is subsequently caused, it is possible to uniform the light-emitting intensity. Therefore, by the driving method of (ii), it is possible to prevent variation in luminance of the panel surface.
Next, a prior-art method of driving a PDP will be specifically discussed with reference to FIGS. 33A to 33E.
One of methods of driving the prior-art AC-PDP 101C (see FIG. 32) is, for example, a driving method in accordance with a prior-art {circle around (1)} disclosed in Japanese Patent Application Laid Open Gazette 7-160218. FIGS. 33A to 33E are timing charts showing driving waveforms of one sub-field period in the driving method. In the following discussion, each of the n row electrodes 104C is termed xe2x80x9crow electrode Xixe2x80x9d (i: 1 to n) and the row electrodes X1 to Xn are termed xe2x80x9crow electrode Xxe2x80x9d as a single unit. Each of the n row electrodes 105C is termed xe2x80x9crow electrode Ykxe2x80x9d (k: 1 to n) and the row electrodes Y1 to Yn are termed xe2x80x9crow electrode Yxe2x80x9d as a single unit driven by a single driving signal. Each of the m column electrodes 108C is termed xe2x80x9ccolumn electrode Wjxe2x80x9d (j: 1 to m) and the column electrodes W1 to Wm are termed xe2x80x9ccolumn electrode Wxe2x80x9d as a single unit.
The sub-field (SF) of FIGS. 33A to 33E is one of a plurality of periods into which one frame (F) for image display are divided, and the sub-field is further divided into three periods, i.e., xe2x80x9creset periodxe2x80x9d, xe2x80x9caddressing periodxe2x80x9d and xe2x80x9csustain discharge period (display period)xe2x80x9d.
In the xe2x80x9creset periodxe2x80x9d, a display history is erased at the ending point of immediately preceding sub-field and priming particles are supplied to increase a discharge probability in the following addressing period. Specifically, a full-screen write pulse of the voltage value that can cause the self-erase discharge on the fall is applied between the row electrode X and the row electrode Y, to erase the display history.
Subsequently, in the xe2x80x9caddressing periodxe2x80x9d, a discharge is made in only a cell to be lighted by matrix selection, to perform a write in the cell. Specifically, as shown in FIGS. 33A to 33E, a scan pulse is sequentially applied to the row electrode Xi and an xe2x80x9caddressing dischargexe2x80x9d which is a write discharge is established between the column electrode Wj and the row electrode Xi in a cell to be lighted. With this discharge as a trigger, a discharge is immediately established between the row electrodes Xi and Yi. At this time, positive or negative wall charges are stacked on the surface of the dielectric layer 106AC (see FIG. 32) of this cell up to the amount sufficient to cause the sustain discharge only by applying the sustain pulse later, as discussed above. On the other hand, in a cell being off, no discharge is established between the row electrodes Xi and Yi lest the addressing discharge should be caused and naturally no wall charge is stacked.
In the xe2x80x9csustain discharge periodxe2x80x9d, applying the sustain pulse between the row electrodes X and Y keeps the sustain discharge of the cell in which a write is made.
In the above prior-art {circle around (1)} adopted is a driving method in which, assuming that the voltage value of the sustain pulse is Vs, a potential of the column electrode W is set to Vs/2. This method is used for starting a stable sustain discharge at the transition from the addressing period to the sustain discharge period. This will be discussed below.
In the driving method of FIGS. 33A to 33E, at the ending point of the addressing period, the negative wall charges are stacked on the sides of the column electrode W and the row electrode Y and the positive wall charges are stacked on the side of the row electrode X. In this state, if the potential of the column electrode Wj during the sustain discharge period is set to 0 V, when the first sustain pulse of the sustain discharge period is applied, a discharge induced by a potential of the wall charges on the sides of the column electrode Wj and the row electrode Xi starts before the sustain discharge is established between the row electrodes Xi and Yi. In this case, there is a possibility of no sustain discharge between the row electrodes Xi and Yi. To avoid this situation, in the prior art {circle around (1)}, the potential of each column electrode Wj is set to Vs/2 to cancel the electric field induced by the wall charges on the side of the column electrode Wj.
Also in the prior art {circle around (1)}, it is suggested that the potential of the column electrode Wj is set to Vs/2 only when the first pulse of the sustain discharge period is applied, and then an output end of the driving circuit of the column electrode Wj is brought into a high impedance. In this case, at the initial stage of the sustain discharge period, the sustain discharge can be stably started and then the power to keep an output of the driving circuit of the column electrode Wj to the potential Vs/2 can be reduced, and therefore it is possible to achieve lower power consumption of the driving circuit. Further, there may be another driving method where the output end of the driving circuit of the column electrode Wj is brought into a high impedance before applying the first sustain pulse, to reduce the amount of wall charges to be stacked on the side of the column electrode Wj during the sustain discharge.
These driving methods, which reduce the ions that fly to the side of the column electrode Wj in the sustain discharge, can also produce an effect of preventing deterioration of the phosphor layer due to ion impact and the like.
As to a gradation display on the AC-PDP, one of the driving methods using a plurality of sub-fields into which one frame is divided as above, known is a method to perform the gradation display by changing the number of sustain pulses in each sub-field into, for example, binary. For example, when the binary is weighted with n sub-fields, 2n-step gradation is achieved.
Though the AC-PDP of FIG. 32 has a structure to extract a display light (visible light) from the side of the front glass substrate 102C, there may be a structure to extract the display light from the rear glass substrate 103C as shown in FIG. 14.
The prior-art method of driving the surface-discharge type AC-PDP, however, has problems of not sufficiently satisfying a requirement of resolving instability of discharge for further improvement in display quality.
(Problem 1)
First, studying improvement of display quality from the viewpoint of the gradation display, there arises the following problem.
The prior-art method of driving the AC-PDP has a problem that a precise gradation display can not be made, in other words, a precise linearity of gradation display can not be achieved, due to very small light emission such as a full-screen erase discharge during the reset period and the addressing discharge (write discharge) during the addressing period. In a prior-art sub-field gradation for 256-level gradation display, since the very small emitted light in each sub-field is added to the emitted light in the sustain discharge, the obtained gradation varies from the desired precise gradation display.
To resolve this problem, it is considered possible in the prior-art driving method that the number of gradation levels is increased by increasing the number of sub-fields in one frame, to make a fine tune of gradation display. When a TV image display is made, for example, however, it is actually difficult to provide a lot of sub-fields in a limited time since the AC-PDP must be driven to complete the display of one image in one field period (16.6 msec), and naturally the number of gradation levels is limited. In the high definition AC-PDP which has increased number of display lines, particularly, it becomes more difficult to increase the number of gradation levels as the number of display lines increases. Therefore, the prior-art driving method has a problem that it is impossible to improve the display quality of the PDP as the precise linearity of gradation display can not be made.
To solve this problem, one of methods of fine tuning of gradation display is a prior art {circle around (2)} suggested in Japanese Patent Application Laid Open Gazettes 8-314405. The prior art {circle around (2)} suggests a driving method in which the number of discharges is controlled by controlling the width of sustain pulse to give a range of gradation display. Specifically, the driving method controls the number of discharges mainly induced by wall charges on the fall of the sustain pulse. The method is based on a fact that when the width of the sustain pulse is small, no self-erase discharge occurs on the fall of the sustain pulse since sufficient wall charges can not be stacked in a voltage supply period, and when the width of the sustain pulse is sufficiently large, a self-erase discharge can occur since sufficient wall charges can be stacked. If the pulse width can be controlled, however, it is difficult to precisely control the discharge by controlling the pulse width in consideration of xe2x80x9ctime lag of dischargexe2x80x9d in the discharge phenomenon.
The above concept, xe2x80x9ctime lag of dischargexe2x80x9d, includes xe2x80x9cstatistic time lagxe2x80x9d representing a time period from a pulse supply to a start of discharge and xe2x80x9cformative time lagxe2x80x9d representing a time period from the start of the discharge to the end thereof.
One of other methods of fine tune of gradation display is a prior art {circle around (3)} suggested in Japanese Patent Application Laid Open Gazettes 7-44127. The prior art {circle around (3)} suggests a driving method using two or more voltage values of sustain pulse according to a display rate, to solve a problem of imprecise gradation display because of deterioration in luminance caused by a voltage drop due to the display rate. Specifically, the driving method is intended to precisely obtain the gradation display that should be originally achieved by providing means for detecting the display rate and means for controlling the potential difference according to the display rate. The prior art {circle around (3)} seems to be effective for high-definition PDP having a large number of display lines, but has problems of complicate circuit configuration and higher cost when two or more power supplies are provided for supplying a sustain voltage.
(Problem 2)
Next discussion will be made on deterioration in display quality caused by disappearance of the sustain discharge.
As discussed above, even if only the discharge mainly induced by externally-applied voltage is performed as the sustain discharge, since a discharge occurs between the row electrode and the column electrode, not the desired surface discharge between the row electrodes, in the initial stage of the sustain discharge period where few space charges exist, there arises a problem that the sustain discharge becomes unstable and then disappears.
Since it is impossible to obtain the desired luminance if the disappearance of the discharge can not be prevented, there arises a problem of imprecise display of image in the AC-PDP.
(Problem 3)
Further, the prior art {circle around (2)} suggests a driving method in which one frame is divided into seven sub-fields and both the discharge mainly induced by externally-applied voltage and the discharge mainly induced by wall charges are used during the sustain discharge period in the fifth to seventh sub-fields. The driving method, however, has a problem that the discharge intermits when the discharge mainly induced by externally-applied voltage and the discharge mainly induced by wall charges are sequentially performed. The reason of this phenomenon is considered as follows. When the discharge mainly induced by wall charges is performed with an increased amount of wall charges caused by the discharge mainly induced by externally-applied voltage, the discharge becomes so large that the wall charges decrease more than needed. Therefore, in the following stage for discharge mainly induced by externally-applied voltage, the discharge can not start due to lack of the necessary amount of wall charges. Further, when a series of discharges are caused with a small amount of space charges, such as in the initial stage of the sustain discharge, the problem of intermittence of the discharge becomes more pronounced.
Since it is impossible to obtain the desired luminance if the intermittence of the discharge can not be prevented, there arises a problem of imprecise display of image in the AC-PDP.
The above problems 1 to 3 are shackles against the requirement of further improvement in display quality through stable discharge and the above requirement can not be properly satisfied without solving the problems 1 to 3.
The charged particles (referring herein to electrons, ions and excited particles) generated in the discharge space have effects of increasing the discharge probability and lowering the firing voltage of the next discharge. In a DC-PDP, as disclosed in Japanese Patent Application Laid Open Gazette 1-274339, for example, an assistant discharge cell is provided adjacently to a display cell, where an assistant discharge is established, to lower a write voltage of the display cell and increase the discharge probability. Since the sustain discharge occurs immediately after the write discharge, it becomes possible to produce a discharge with a lower applied voltage as the firing voltage is lowered due to existence of the charged particles. To stop the discharge, it is necessary only to provide an idle period of the sustain pulse enough to extinguish the charged particles and not necessary to perform the erase operation to extinguish the wall charges like in the AC-PDP. The lifetime of the charged particles is about 10 xcexcsec to 20 xcexcsec, though the lifetime depends on the pressure of filled gas, the kind of gas and the cell structure. Such a memory function of the DC-PDP using the charged particles is referred to as pulse memory function (effect).
FIG. 15 is a timing chart showing voltage waveforms of one sub-field in the prior-art method of driving the plasma display panel disclosed in Japanese Patent Application Laid Open Gazette 7-160218 (the prior art {circle around (1)}). One sub-field consists of the reset period for erasing the display history, the addressing period for selecting a cell to be lighted and the sustain discharge period (display period) performed a specified number of times to obtain a predetermined luminance. FIG. 15 shows the waveforms of voltages applied to a column electrode Wj (j: 1 to m), a first row electrode Xi (i: 1 to n) and second row electrodes Y1, Y2 and Yn in this order from above.
In the reset period, first, a full-screen write pulse Pxp is applied to the first row electrodes X1 to Xn connected in common to the full screen at a time a of FIG. 15. The full-screen write pulse Pxp is referred to as a xe2x80x9cpriming pulsexe2x80x9d. Since the full-screen write pulse Pxp is set not less than the firing voltage between the first and second row electrodes Xi and Yi and applied for a sufficiently long time (or a sufficiently large pulse width) of about 10 xcexcsec, all the cells are discharged to emit a light, regardless of emission or non-emission in the preceding sub-field. Though a voltage pulse Pwp is applied to the column electrode Wj at this time. This is intended to reduce a potential difference between the first row electrode X and the column electrode W so that it may become hard to cause a discharge between the electrodes X and W. The voltage pulse Pwp is set to half of the voltage across the electrodes X and W. When the full-screen write pulse Pxp is applied, a strong discharge occurs between the electrodes Xi and Yi and ends with a large amount of wall charges stacked therebetween. Subsequently, when the full-screen write pulse Pxp falls at a time b of FIG. 15 and no voltage is applied between the first row electrode X and the second row electrode Y, an electric field is generated by the wall charges stacked by that full-screen write pulse Pxp between the electrodes X and Y. Since the electric field exceeds (is larger than) the firing voltage, the self-erase discharge occurs to extinguish the wall charges.
Thus, all the cells are written and then erased, regardless of whether there are any wall charges or no wall charge, to have no wall charge, being reset.
After the reset period, at a time c of FIG. 15, few negative electric charges are left on the first row electrode X and few positive electric charges are left on the second row electrode Y The amount of left electric charges depends on the characteristics of a cell, and specifically a small amount of wall charges are left on a cell having a low firing voltage (easy to light) and a large amount of wall charges are left on a cell having a high firing voltage (difficult to light). This works in a converse direction to relieve variation of the cells in the next light emission. Further, in the discharge space left are a slight amount of charged particles generated through the discharge by the preceding full-screen write pulse Pxp. The charged particles no longer have the effect of lowering the firing voltage and work to ensure a discharge in the next write. In other words, this serves as a priming for the write discharge. This is the reason why the full-screen write pulse Pxp is referred to as a priming pulse. Therefore, this method using a pulse which has both the priming effect and the erasing effect and further has a xe2x80x9cself-control functionxe2x80x9d that relieves the variation of the cells after the erase, is a rather good one for a stable operation of the plasma display panel. Further, since the priming effect has a time constant of several msec, by applying the full-screen write pulse Pxp every several sub-fields and an erase pulse having a narrow width or low voltage value to the remaining sub-fields, only cells lighted in the preceding sub-field may be discharged and erased. The Japanese Patent Application Laid Open Gazette 8-278766 discloses a method utilizing a fact that the cells have different time lags of discharge depending on whether lighted or not in the preceding sub-field, specifically, a method of applying a pulse having the same voltage as the priming pulse and narrower width to reduce the number of full-screen light emissions, thereby improving a contrast.
In the addressing period, a negative scan pulse Scyp is sequentially applied to the second row electrodes Y1 to Yn independently of on another to make a scan. On the other hand, a positive addressing pulse Awp according to image data is applied to the row electrode Wj. With the scan pulse Scyp applied to the second row electrodes Yi and the addressing pulse Awp applied to the column electrode Wj, a predetermined cell on the screen can be selected by matrix. Since the total voltage value of the scan pulse Scyp and the addressing pulse Awp is set not less than the firing voltage between the electrodes Y and W of the cell, a discharge occurs between the electrodes Yi and Wj in the cell to which the scan pulse Scyp and the addressing pulse Awp are simultaneously applied. Further, in the addressing period, the first row electrode X (all the first row electrodes X1 to Xn) is kept positive in voltage value. This voltage value is so set as not to cause any discharge between the electrodes X and Y even together with the voltage value of the scan pulse Scyp but as to cause a discharge between the electrodes X and Y when a discharge occurs between the electrodes Y and W, with this discharge as a trigger. The discharge between the electrodes X and Y using the discharge between the electrodes Y and W as a trigger is referred to as xe2x80x9cwrite sustain dischargexe2x80x9d. The write sustain discharge causes the wall charges to be stacked on the first and second row electrodes X and Y.
After a full-screen scan in the addressing period, the sustain pulse Sp is applied to the full screen and the sustain discharge is caused only in the cells which are selected in the addressing period and on which the wall charges are stacked. In the next sub-field, the full-screen write pulse Pxp is applied to all the cells in the reset period, to perform a reset.
Such a driving method as above separating a sub-field into the addressing period and the sustain discharge period for image display on the whole screen of the AC-PDP is termed xe2x80x9caddressing/sustain separation methodxe2x80x9d, which is a general and well-known technique.
Next, an efficiency of the AC-PDP will be discussed. FIG. 16 is a graph of a relation between a current density and a light-emitting efficiency shown in xe2x80x9cThe State of The Art in Plasma Display xe2x80x9d (by Shigeo Mikoshiba, ED Research, issued in 1996). As shown in FIG. 16, it is well known that the efficiency rises as the current density falls. As a method of lowering the current density known are a method of reducing a driving voltage and that of forcedly falling an externally-applied voltage before the discharge ends (flow of a discharge current is completed). As the former known is a method disclosed in, for example, Japanese Patent Application Laid Open Gazette 3-219528 (see FIGS. 17A and 17B), which uses an assistant electrode 102A before a main electrode 104A and reduces a voltage of the main electrode 104A by using the discharge of the assistant electrode 102A as a trigger. The latter is termed Townsend discharge. In Japanese Patent Application Laid Open Gazette 7-134565, for example, after stabilizing the discharge by increasing the width of only the first pulse in the sustain discharge period, pulses having a very small width, from the second pulse, are applied and fallen before the discharge current is finished, to lower the current density. Further, other than these methods, it may be considered that the self-erase discharge is caused to reduce the wall charges and lower the effective voltage (applied voltage and wall charges). FIG. 18 illustrates a relation between an externally-applied voltage and a light-emitting efficiency. Though the voltage value differs depending on the panel structure, the filled gas and the kind of gas, the PDP having a structure where electrodes are covered with a dielectric obtains the same characteristics line qualitatively. It can be seen that the efficiency falls on the low-voltage side and the efficiency conversely rises on the high-voltage side as the voltage rises. The rise on the high-voltage side is an area where the self-erase occurs.
One of the driving methods using the self-erase discharge in the sustain discharge period is disclosed in, for example, Japanese Patent Application Laid Open Gazette 8-314405. FIG. 24 shows voltage waveforms in this method. This method is used in a stationary state where the firing voltage is not influenced by the charged particles, in which sufficient wall charges higher in voltage than the firing voltage are stacked in the voltage supply period and an interval between consecutive pulses (hereinafter, referred to as xe2x80x9cidle periodxe2x80x9d) in the sustain discharge period is brought into a ground potential, to cause the self-erase discharge during the idle period. This method has a characteristic feature that the charged particles are not drawn to the display electrode because of no externally-applied voltage in the idle period, and as a result, there is no ion bombardment and the number of light emission is twice the number of voltage supply. Further, this self-erase discharge does not occur when the pulse width is narrowed to reduce the amount of stacked wall charges nor when the applied voltage is lowered. Thus, controlling the self-erase discharge is helpful for the gradation display.
To enhance the efficiency through improvement of the driving method, it is necessary to use the voltage near the lower limit or upper limit of the margin as shown in FIG. 18. There is a possibility of a problem that a cell which should be lighted can not be lighted in the low-voltage area and a cell which should not be lighted is lighted in the high-voltage (self-erase) area. Considering actual mass productivity of the PDP, to produce a panel having a wide margin (good yield), it is necessary to select the voltage near an intermediate as the operating point, using an area with very poor efficiency.
Furthermore, the self-erase discharge produced by applying a high-voltage pulse, which is high in voltage, causes not only between the electrodes X and Y but also between the electrode W and the electrode X or Y Without the self-erase discharge, even if the discharge between the electrode W and the electrode X or Y is once established, an AC driving can not be achieved as the wall charges on the electrode W work as a mask. Therefore, no discharge occurs again. When the self-erase discharge is used, the wall charges generated by the discharge between the electrode W and the electrode X or Y on the rise induce another discharge on the fall and disappear, sustaining the discharge. The discharge between the electrode W and the electrode X or Y causes not only wrong addressing but also deterioration of the phosphor caused by using it as a cathode (causing a sputter).
The high-voltage driving further has a problem of increasing a circuit loss (power loss) which is in proportion to the square of the voltage relative to a capacitive load like the PDP.
Even if it is intended to actively use the self-erase discharge, since the electrode has the ground potential in the idle period, the discharge taking place on the fall of the applied pulse is induced only by the wall charges and therefore the magnitude of the discharge is necessarily limited.
The prior-art driving method of achieving a high contrast also has a problem. To achieve a high contrast, as discussed earlier, for example, a full-screen light emission is made every several sub-fields, and a cell lighted in the preceding sub-field is lighted and erased in each of the remaining sub-fields. In this case, if the xe2x80x9cself-control functionxe2x80x9d of the self-erase discharge is used, it is necessary to narrow the pulse width. At this time, because of a small margin of the pulse width, a cell not lighted in the preceding sub-field is lighted even if the pulse width slightly exceeds the margin. Further, in some cells that produce an incomplete discharge, the discharge ends before the wall charges enough to perform the self-erase are stacked, to cause a wrong discharge. If the erase without the self-erase discharge (e.g., narrow-width erase) is made, there is a difference in a state of residual wall charges between the sub-field in which a full-screen light emission is made and the sub-field in which it isn""t made, and the sub-fields thereby have different margins.
FIG. 25 is a chart showing a prior-art driving method disclosed in Japanese Patent Application Laid Open Gazette 7-134565, where the assistant discharge is established before the sustain discharge. This uses the xe2x80x9caddressing/sustain separation methodxe2x80x9d. This method pays attention to the fact that the early stage of the sustain discharge is unstable in a cell having a long time from the end of addressing discharge to the start of sustain discharge, provides the assistant discharge before the sustain discharge. Specifically, considering the time lag of discharge, a pulse immediately before the sustain discharge is set to have a sufficiently large pulse width or a high voltage.
When the discharge mainly induced by wall charges (a second discharge) on the fall of the pulse is used for the sustain discharge, there arises a problem that it becomes hard to cause the next sustain discharge as the wall charges decrease as compared with the sustain discharge using only the discharge mainly induced by externally-applied voltage (a first discharge). In the early stage of the sustain discharge, particularly, the discharge once occurs and then disappears because of few space charges. That needs an unnecessary high sustain voltage and further narrows a voltage margin necessary for stable discharge.
Furthermore, since the last stage of the sustain discharge is mainly induced by wall charges, there arises a problem that it is hard to cause the next erase pulse as there are few wall charges in this state.
The present invention is directed to a method of driving a plasma display panel.
According to a first aspect of the present invention, in the method of driving the plasma display panel which comprises first and second electrodes both covered with dielectric and a third electrode provided in a direction to cross at least one of the first and second electrodes in a cell, a sustain discharge comprises a first discharge and a second discharge, the first discharge is mainly induced by externally-applied voltage, the second discharge is mainly induced by wall charges generated by the first discharge, the sustain discharge is performed a specified number of times between the first and second electrodes to obtain a predetermined luminance, and the second discharge in the sustain discharge utilizes charged particles generated by the first discharge.
According to a second aspect of the present invention, in the method of the first aspect, the sustain discharge utilizes a memory effect of the charged particles.
According to a third aspect of the present invention, in the method of the first aspect, a sustain discharge pulse has a pulse width of 1.6 xcexcsec or less.
According to a fourth aspect of the present invention, in the method of the first aspect, an idle period between pulses to obtain the first discharge in the sustain discharge is 0.8 xcexcsec or more.
According to a fifth aspect of the present invention, in the method of the first aspect, a fall of pulse in the sustain discharge is 300 nsec or less.
According to a sixth aspect of the present invention, in the method of the first aspect, an assistant pulse is applied in a direction to actively utilize the second discharge up to a value at which a polarity of residual wall charges is not reversed at the end of the second discharge.
According to a seventh aspect of the present invention, in the method of the sixth aspect, the assistant pulse is generated negatively to a ground potential on a fall of the sustain pulse.
According to an eighth aspect of the present invention, in the method of the sixth aspect, the assistant pulse is generated positively to the ground potential on a fall of the sustain pulse.
According to a ninth aspect of the present invention, in the method of driving a plasma display panel comprising at least one electrode which is covered with dielectric, a sustain discharge comprises a first discharge and a second discharge, the first discharge is mainly induced by externally-applied voltage, the second discharge is mainly induced by wall charges generated by the first discharge, the sustain discharge is performed a specified number of times between the first and second electrodes to obtain a predetermined luminance, and a group of pulses causing a first assistant discharge are applied in a form not to induce the second discharge between an addressing discharge to select a predetermined cell and the sustain discharge.
According to a tenth aspect of the present invention, in the method of the ninth aspect, the group of pulses causing the first assistant discharge each have a pulse width larger than that of a group of pulses causing the sustain discharge.
According to an eleventh aspect of the present invention, in the method of the ninth aspect, the group of pulses causing the first assistant discharge each have an idle period narrower than that of the group of pulses for the sustain discharge.
According to a twelfth aspect of the present invention, in the method of the first aspect, a group of pulses causing a first assistant discharge is applied in a form not to induce said second discharge between an addressing discharge to select a predetermined cell and said sustain discharge, and the group of pulses causing the first assistant discharge each have an idle period narrower than that of the group of pulses for the sustain discharge.
According to a thirteenth aspect of the present invention, in the method of the ninth aspect, the sustain discharge in a sub-field having little luminance information includes only the first assistant discharge.
According to a fourteenth aspect of the present invention, in the method of driving the surface-discharge type AC plasma display panel which comprises: first and second electrodes in a pair; a third electrode provided in a direction to cross the first and second electrodes; and a dielectric layer covering the first and second electrodes to stack wall charges, a sustain discharge period comprises a first period in which a first discharge mainly induced by externally-applied voltage across the first and second electrodes is caused; a second period following the first period; and a third period following the second period, in which the first discharge and a second discharge mainly induced by the wall charges are caused in this order, and a potential of the third electrode is switched between a first potential and a second potential lower than the first potential and higher than a ground potential in the second period.
In the method of driving the plasma display panel of the first aspect, utilizing the charged particles generated in the first discharge makes it possible to cause the second discharge with a low voltage.
In the method of driving the plasma display panel of the second aspect, utilizing the charged particles makes it possible to keep the sustain discharge with a low voltage.
In the method of driving the plasma display panel of the third aspect, specifying that the width of the sustain pulse is 1.6 xcexcsec or less allows better use of the charged particles generated in the first discharge to cause the second discharge, to improve the light-emitting efficiency.
In the method of driving the plasma display panel of the fourth aspect, specifying that the idle period between the sustain pulses is 0.8 xcexcsec or more allows the second discharge to be intensified, to improve the light-emitting efficiency.
In the method of driving the plasma display panel of the fifth aspect, specifying that the fall of pulse is 300 nsec or less allows the second discharge to be intensified, to improve the light-emitting efficiency.
In the method of driving the plasma display panel of the sixth aspect, since the sustain discharge includes the first discharge mainly induced by externally-applied voltage and the second discharge mainly induced by wall charges and the assistant pulse is applied in a direction to actively utilize the second discharge up to the value at which the polarity of residual wall charges is not reversed at the end of the second discharge, the second discharge is intensified, to improve the light-emitting efficiency.
In the method of driving the plasma display panel of the seventh aspect, generating the assistant pulse negatively to the ground potential on the fall of the sustain pulse allows the second discharge to be intensified, to improve the light-emitting efficiency.
In the method of driving the plasma display panel of the eighth aspect, generating the assistant pulse positively to the ground potential on the fall of the sustain pulse allows the second discharge to be intensified, to improve the light-emitting efficiency.
By the method of driving the plasma display panel of the ninth aspect, a large voltage margin can be obtained when the second discharge mainly induced by wall charges is used as the sustain discharge and a stable sustain discharge is achieved with high efficiency.
By the method of driving the plasma display panel of the tenth aspect, a large voltage margin can be obtained when the second discharge mainly induced by wall charges is used as the sustain discharge and a stable sustain discharge is achieved with high efficiency.
By the method of driving the plasma display panel of the eleventh and twelfth aspects, a large voltage margin can be obtained and a stable sustain discharge is achieved with high efficiency when the second discharge mainly induced by wall charges is used as the sustain discharge.
In the method of driving the plasma display panel of the thirteenth aspect, since the sustain discharge in the sub-field having little luminance information includes only the first assistant discharge, the gradation display can be achieved without lengthening any field cycle.
The driving method of the fourteenth aspect, which switches the potential of the third electrode between the first and second potentials, can control the amount of self-erase discharge at the second discharge (the discharge mainly induced by wall charges) in a case where both the first and second discharges are used. Therefore, no excessive self-erase discharge occurs in the transition from the first period to the second period, and it is possible to prevent a disappearance of discharge due to this excessive discharge and achieve a stable discharge. The driving method of the ninth aspect can improve the display quality of the PDP device.
Since the driving method of the fourteenth aspect can prevent the disappearance of discharge due to the excessive self-erase discharge, the method also produces a derivative effect of eliminating the necessity for applying the relatively high sustain voltage between the first and second electrodes to achieve a stable margin of the sustain voltage.
An object of the present invention is to provide a method of driving a plasma display panel which uses a discharge mainly induced by wall charges to enhance the light-emitting (discharge) efficiency and increases a margin of discharge condition to obtain a stable discharge. To achieve this main object, the present invention has the following detailed sub-objects.
The first object of the present invention is to improve the efficiency of the PDP, without increasing the circuit loss or reducing the margin, by producing a discharge mainly induced by wall charges on a fall with a low voltage and to the maximum which has been conventionally caused by applying a high voltage.
The second object of the present invention is to prevent a discharge between the electrode W and the electrode X or Y which is sustained by using a self-erase pulse during the sustain discharge period.
The third object of the present invention is to equalize the operating points of both a sub-field using a full-screen light emission and that not using it by using the discharge mainly induced by wall charges for the erase and relieve the variation of cells by using the xe2x80x9cself-control functionxe2x80x9d of the discharge mainly induced by wall charges.
The fourth object of the present invention is to provide a method of driving a plasma display panel, which can prevent an unnecessary decrease of margin and ensure an erase operation in a case of sustain discharge using the second discharge mainly induced by wall charges.
The fifth object of the present invention is to provide a method of driving a surface-discharge type AC-PDP which achieves a fluent gradation display through fine tune of light-emitting luminance during the sustain discharge period.
The sixth object of the present invention is to provide a method of driving a surface-discharge type AC-PDP, which use both the discharge mainly induced by externally-applied voltage and the discharge mainly induced by wall charges during the sustain discharge period, intended to stabilize both the discharges by controlling the magnitude of discharge mainly induced by wall discharges.
The seventh object of the present invention is to provide a method of driving a surface-discharge type AC-PDP intended to reliably start the discharge in the initial stage of the sustain discharge period and then make a stable transition to the desired surface discharge.
The eighth object of the present invention is to provide a method of driving a surface-discharge type AC-PDP intended to achieve the fifth to seventh objects.
The ninth object of the present invention is to provide a method of driving a surface-discharge type AC-PDP which obtains a markedly-improved display quality through achieving the fifth to seventh objects.
According to a fifteenth aspect of the present invention, in the method of driving the plasma display panel which comprises first and second electrodes both covered with dielectric and a third electrode provided in a direction to cross at least one of the first and second electrodes in a cell, a sustain discharge which is performed a specified number of times between said first and second electrodes to obtain a predetermined luminance includes a first discharge mainly induced by externally-applied voltage and a second discharge mainly induced by generated wall charges.
According to a sixteenth aspect of the present invention, the method of driving the plasma display panel separates a sub-field into the addressing period in which cells to be lighted are optionally selected and the sustain discharge period in which the discharge is established simultaneously on the selected cells a specified number of times.
According to a seventeenth aspect of the present invention, in the method of driving the plasma display panel, the sustain discharge period has a time period in which the third electrode is in a floating state.
According to an eighteenth aspect of the present invention, in the method of driving the plasma display panel, the sustain pulse generated by the first and second discharges is used as an erase pulse.
According to a nineteenth aspect of the present invention, in the method of driving the plasma display panel, the group of pulses for the first assistant discharge each have a falling rate slower than that of the group of pulses for the sustain discharge.
According to a twentieth aspect of the present invention, in the method of driving the plasma display panel comprising at least one electrode which is covered with dielectric, which performs a sustain discharge including the first discharge mainly induced by externally-applied voltage and the second discharge mainly induced by generated wall charges a specified number of times to obtain a predetermined luminance, a group of pulses for a second assistant discharge pulse are applied in a form not to induce the second discharge between the sustain discharge and an erase discharge.
According to a twenty-first aspect of the present invention, in the method of driving the plasma display panel, the group of pulses for the second assistant discharge each have a pulse width larger than that of the group of pulses for the sustain discharge.
According to a twenty-second aspect of the present invention, in the method of driving the plasma display panel, the group of pulses for the second assistant discharge each have an idle period narrower than that of the group of pulses for the sustain discharge.
According to a twenty-third aspect of the present invention, in the method of driving the plasma display panel, the group of pulses for the second assistant discharge each have a falling rate slower than that of the group of pulses for the sustain discharge.
According to a twenty-fourth aspect of the present invention, in the method of the sixth aspect, the sustain discharge in a sub-field having little luminance information includes only a second assistant discharge.
According to a twenty-fifth aspect of the present invention, in the method of driving the surface-discharge type AC plasma display panel which comprises first and second electrodes in a pair; a third electrode provided in a direction to cross the first and second electrodes; and a dielectric layer covering the first and second electrodes to stack wall charges, a potential of the third electrode is switched between a ground potential and a first potential which is predetermined during a sustain discharge period.
According to a twenty-sixth aspect of the present invention, in the method of driving the surface-discharge type AC plasma display panel which comprises first and second electrodes in a pair; a third electrode provided in a direction to cross the first and second electrodes; and a dielectric layer covering the first and second electrodes to stack wall charges, a potential of the third electrode is switched between a ground potential and a first potential which is predetermined in a first period which is an initial stage of a sustain discharge period, and a potential of the third electrode is set to a second potential lower than the first potential in a second period of the sustain discharge period following the first period.
The present invention is directed to a driving circuit for a surface-discharge type AC plasma display panel. According to a twenty-seventh aspect of the present invention, the driving circuit for the surface-discharge type AC plasma display panel comprises a driving circuit for the third electrode generating a driving signal for driving the third electrode and outputting the driving signal to the third electrode by the method of driving the surface-discharge type AC plasma display panel.
According to a twenty-eighth aspect of the present invention, the driving circuit for the surface-discharge type AC plasma display panel further comprises a resistor connected in parallel to the driving circuit for the third electrode.
According to a twenty-ninth aspect of the present invention, the surface-discharge type AC plasma display panel is driven by the method of driving the surface-discharge type AC plasma display panel.
In the method of driving the plasma display panel of the fifteenth aspect, since the sustain discharge which is performed a specified number of times between the first and second electrodes to obtain a predetermined luminance includes the first discharge mainly induced by externally-applied voltage and the second discharge mainly induced by generated wall charges, it is possible to improve a light-emitting efficiency.
In the method of driving the plasma display panel of the sixteenth aspect, by separating the sub-field into the addressing period in which cells to be lighted are selected and the sustain discharge period in which the discharge is established simultaneously on the selected cells the specified number of times, the sustain pulse in the sustain discharge period can be changed easily and independently of the addressing period.
In the method of driving the plasma display panel of the seventeenth aspect separating the sub-field into the addressing period and the sustain discharge period, since the sustain discharge period has the time period in which the third electrode is in a floating state, it is possible to prevent an unnecessary discharge between the third electrode and the first or second electrode.
In the method of driving the plasma display panel of the eighteenth aspect, by using the sustain pulse generated by the first and second discharges as the erase pulse, a stable display can be achieved without any additional erase operation.
By the method of driving the plasma display panel of the nineteenth aspect, a large voltage margin can be obtained and a stable sustain discharge is achieved with high efficiency when the second discharge mainly induced by wall charges is used as the sustain discharge.
The method of driving the plasma display panel of the twentieth aspect achieves a reliable erase when the second discharge mainly induced by wall charges is used as the sustain discharge.
The method of driving the plasma display panel of the twenty-first aspect achieves a reliable erase when the second discharge mainly induced by wall charges is used as the sustain discharge.
The method of driving the plasma display panel of the twenty-second aspect achieves a reliable erase when the second discharge mainly induced by wall charges is used as the sustain discharge.
The method of driving the plasma display panel of the twenty-third aspect achieves a reliable erase when the second discharge mainly induced by wall charges is used as the sustain discharge.
In the method of driving the plasma display panel of the twenty-fourth aspect, since the sustain discharge in the sub-field having little luminance information includes only the second assistant discharge, the gradation display can be achieved without lengthening any field cycle.
The driving method of the twenty-fifth aspect can control the magnitude of the sustain discharge, i.e., a light-emitting intensity of the PDP, only by switching the potential of the third electrode between the ground potential and the predetermined first potential in the sustain discharge period. Two kinds of light emissions of different intensities are thereby produced and the number of light emissions is controlled for each kind to make a fine tune of luminance. Therefore, the driving method of the twenty-fifth aspect can precisely realize a linearity of display gradation of the PDP, to achieve a fluent gradation display.
Further, the driving method of the twenty-fifth aspect can reduce the number of supplies of the sustain discharge pulse, as compared with the prior-art driving method of the gradation display of the same level. That produces a time surplus in one frame or one sub-field. When this time surplus is allocated to an increase of the addressing period (write period), the width of the write pulse can be increased, to avoid a write failure and the like due to the time lag of discharge.
From the fact that the time surplus is produced, it is found that the driving method of the twenty-fifth aspect achieves a faster driving than the prior-art driving method. In a case of TV display, for example, where it is required to display an image in a constant time period, i.e., one field (=16.6 msec), the driving method of the twenty-fifth aspect, which performs a faster driving, can achieve an image display in the above time period even if the number of display lines increases. Therefore, the driving method of the twenty-fifth aspect produces an effect of driving a PDP device having more display lines (of higher definition) than the prior-art PDP.
Furthermore, the driving method of the twenty-fifth aspect can optionally set the total number of sustain discharge pulses as compared with the prior-art driving method. Therefore, the method achieves the maximum luminance in an available time length (one field) without deteriorating gradation, as compared with the prior-art driving method.
Thus, the driving method of the twenty-fifth aspect can improve the display quality of the PDP device.
The driving method of the twenty-sixth aspect, which controls the discharge in detail at the initial stage (the first period) of the sustain discharge period, can prevent the disappearance of discharge and the like, to achieve a stable discharge. Specifically, the discharge is actively caused between the third electrode and the first or second electrode for the charge distribution condition at the ending point of the immediately preceding addressing period in the first period, to generate a large amount of space charges. After that, by making a transition to the surface discharge between the first and second electrodes, it becomes possible to perform a stable sustain discharge. Therefore, the driving method of the twenty-sixth aspect can improve the display quality of the PDP device.
The driving circuit of the twenty-seventh aspect produces an effect of improving the display quality.
The driving circuit of the twenty-eighth aspect produces an effect of improving the responsivity at the switching of the potential of the third electrode by discharging the electric charges of the third electrode through the resistor.
The surface-discharge type AC plasma display panel of the twenty-ninth aspect produces the same effect as the fifteenth, twenty-fifth and twenty-sixth aspects.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.